Authorities are investigating the cause of a massive pileup early Sunday morning south of Gainesville, Florida, on Interstate 75 , where a long line of cars and trucks collided one after another on a dark highway so shrouded in haze and smoke that drivers were blinded.At least 10 people were killed and another 18 were taken to a nearby hospital, Shands at the University of Florida. As of Sunday night, six patients remained in the trauma center and three others admitted through the emergency room remained.

The interstate had been closed for a time before the accidents because of a mixture of fog and heavy smoke from a brush fire that may have been intentionally set. The decision to reopen it early Sunday will certainly be a focus of investigators, as will the question of how the fire may have started.

Authorities reopened the southbound lanes of I-75 around 11 a.m. Monday, the north-south highway that runs virtually the entire length of Florida. Complicating matters was that some of the road's asphalt melted. The northbound lanes were reopened late Sunday afternoon. (For information on Florida highway closures, click here.)

"Our standard operating procedure is to get the road open as quickly as possible but let's not forget we have 10 people who are not with us today," Lt. Patrick Riordan, a Florida Highway Patrol spokesman, said Sunday evening. "So we are going to take our time assessing the situation."

The pileups happened around 3:45 a.m. Sunday on both sides of I-75. When rescuers first arrived, they could only listen for screams and moans because the poor visibility made it difficult to find victims in wreckage that was strewn for nearly a mile.

At least a dozen cars and six tractor-trailers were involved, and some burst into flames.

Hours later, twisted, burned-out vehicles were scattered across the pavement, with smoke still rising from the wreckage.

Cars appeared to have smashed into the big rigs and, in one case, a motor home. Some cars were crushed beneath the heavier trucks.. One tractor-trailer was burned down to its skeleton, charred pages of books and magazines in its cargo area. And the tires of every vehicle had burned away, leaving only steel belts.

Before Steven Camps hit the fog bank, a friend who was driving ahead of him in a separate vehicle called to warn of the road conditions. The friend said he had just seen an accident and urged Camps to be careful as he approached the Paynes Prairie area, just south of Gainesville.

A short time later, Camps said, traffic stopped along the northbound lanes.

"You couldn't see anything. People were pulling off the road," he said.

Camps said he began talking about the road conditions to a man in the car stopped next to him when another vehicle hit that man's car.

The man's vehicle was crushed under a semi-truck stopped in front of them. Camps said his car was hit twice, but he and another friend were able to jump out. They took cover in the grass on the shoulder of the road.

All around them, cars and trucks were on fire, and they could hear explosions as the vehicles burned.

"It was happening on both sides of the road, so there was nowhere to go. It blew my mind," he said, explaining that the scene "looked like someone was picking up cars and throwing them."

Authorities had not released the names of victims Sunday evening, but said one passenger car had four fatalities. A "tour bus-like" vehicle also was involved in the pileup, police said.

All six lanes of the interstate were closed most of Sunday as investigators surveyed the site and firefighters put out the last of the flames. Some traffic was being diverted onto U.S. 301 and State Road 27, Riordan said. The northbound lanes were reopened at about 5:30 p.m.

At some point before the pileup, police briefly closed the highway because of fog and smoke. The road was reopened when visibility improved, police said. Riordan said he was not sure how much time passed between the reopening of the highway and the first crash.

A spokeswoman for the Florida Forest Service, Ludie Bond, said the fire began Saturday, and investigators were trying to determine whether the blaze had been intentionally set. She said there were no controlled burns in the area and no lightning.

Bond also said the fire had burned 62 acres and was contained but still burning Sunday. A similar fire nearby has been burning since mid-November because the dried vegetation is so thick and deep. No homes are threatened.

Four years ago, heavy fog and smoke were blamed for another serious crash.

In January 2008, four people were killed and 38 injured in a series of similar crashes on Interstate 4 between Orlando and Tampa, about 125 miles south of Sunday's crash. More than 70 vehicles were involved in those crashes, including one pileup that involved 40 vehicles.